Reconfiguration of sediment fungal communities following coastal aquaculture pond restoration: coupling diversity shifts, assembly mechanisms and network stability.

Restoring abandoned aquaculture ponds to coastal wetlands is an important strategy for recovering biodiversity and ecosystem functions, yet the responses of sediment fungal communities during this transition remain poorly understood. Here, we compared fungal communities in active aquaculture ponds and restored tidal wetlands along the Jiangsu coastline to evaluate shifts in community structure, functional traits, and stability. Restoration substantially reduced clay content and ammonium nitrogen, shifting sediments from eutrophic and reduced conditions toward more oxidized and oligotrophic states. Fungal communities underwent pronounced taxonomic reconfiguration, with Ascomycota increasing from 35.3% to 80.8%, while richness and diversity exhibited a lagged recovery. Functional annotation revealed strong guild-level shifts, including increases in pathotrophs (22.7% to 47.7%) and symbiotrophs (10.8% to 17.7%) and marked differentiation within saprotrophic subgroups, indicating functional realignment under changing nutrient and habitat conditions. Community assembly transitioned from deterministic environmental filtering to stochastic dynamics, as reflected by an increase in the normalized stochasticity ratio from 15.9% to 75.2%, ecological drift from 34.7% to 90.1%, and a rise in habitat generalists from 37.4% to 77.8%, consistent with significant niche expansion. Co-occurrence networks shifted from dense, highly aggregated structures to more heterogeneous and modular configurations, indicating reduced homogenized co-fluctuation and enhanced interaction differentiation. Network stability also improved, with cross-module connectors increasing from 10 to 64 and Ascomycota serving as key mediators of inter-module connectivity. Overall, this study reveals how structural, functional, and interactional processes are associated with early fungal recovery in restored coastal wetlands, offering insight into mechanisms that may support community stabilization and ecosystem resilience.